The present invention relates to a stencil printing method and to an apparatus for the same, and more specifically relates to a stencil printing method using a novel type of plate having numerous fine apertures that expand or narrow in response to a stimulus selected from heat and light, and to an apparatus for the same.
Commonly prevailing as a digital duplicator high in printing speed and low in running cost is a printing machine in which a master is produced by melt-perforating a thermoplastic resin film layer of a heat sensitive stencil sheet by use of a heating means such as a thermal printing head which generates heat in a dot-like pattern in accordance with character or image information converted into electric signals, and in which the stencil sheet is wound around a circumferential surface of a printing drum so that an ink is transferred from the printing drum to a printing sheet through the perforated stencil sheet.
The digital duplicator known in the art requires a device for storing and conveying the heat-sensitive stencil sheet as well as a used-stencil discharging device. When printing is performed based on a new original, a used-sheet must be discarded. Usually, the used-stencil is temporarily stored in a used-stencil discharge box, and then is disposed when the box is full of used-stencils. This is because, in the conventional stencil printing, stencil sheets used as printing plates cannot be regenerated or reused.
An object of the present invention is to provide a novel stencil printing plate that can be used in place of conventional stencil sheets, thereby providing a novel stencil printing method and an apparatus for the same, which solve the aforementioned problems of the conventional technology, and which eliminate provision and disposal of heat-sensitive stencil sheets.
In accordance with the present invention, the object above is accomplished by a stencil printing method comprising providing a film which is made of a polymeric material that shrinks in response to a stimulus selected from heat and light, said film having numerous fine apertures in cross sectional direction thereof, giving said stimulus to said film in such a manner that a desired image is reproduced to expand said apertures selectively at sites to which said stimulus is given, and allowing an image forming material to pass through the thus expanded apertures to transfer the image forming material to a recording medium.
In other words, the printing method according to the present invention comprises providing a stencil printing plate comprising a film made of a polymeric material which shrinks in response to a stimulus selected from heat and light and in which numerous fine apertures are previously provided in the film in cross sectional direction thereof, obtaining a master by providing said stimulus to said film to trace a desired image thereon and thereby selectively expand the apertures, and transferring an image forming material to a recording medium by passing the image forming material through the expanded apertures of the thus obtained master.
Hence, in accordance with another aspect of the present invention, there is provided a stencil printing plate comprising a film which is made of a polymeric material that shrinks in response to a stimulus selected from heat and light, said film having numerous fine apertures in cross sectional direction thereof.
The stencil printing plate according to the present invention is characterized in that when the stimulus of heat or light is given to the film, the film of the plate shrinks. Thus, in response to the stimulus, the surface of the film shrinks while expanding the apertures so that an image forming material can easily pass through the apertures. Size of each of the apertures may be such that the image forming material is not easily passed therethrough when the film is not given the stimulus. More specifically, the size can be properly selected depending on the physical properties, e.g., viscosity, etc., of a printing ink or other image forming materials.
Preferably, the polymeric material constituting the present stencil printing plate is further characterized in that it expands in response to another stimulus. In this case, in response to this stimulus, the surface of the film expands to narrow the apertures, and thereby hinders the passage of the image forming material. Thus, such a polymeric material is advantageous in that the passage of image forming materials can be inhibited irrespective of viscosity and other physical properties of the image forming materials.
Accordingly, the apertures of the plate of the present invention can be reversibly switched from a state in which an ink is allowed to pass to a state in which the passage of the ink is hindered, in response to different types of stimuli. In other words, the apertures of the plate can be reversibly switched from an opened state to a closed state. Thus, the plate can be regenerated or prepared for re-use in the next printing by closing all of the apertures even after it is once made into a master and used for printing. In order to close the apertures and regenerate the plate, the stimulus given to shrink the polymeric material constituting the film only has to be removed to cancel out the shrinking state, or alternatively, the aforementioned another stimulus capable of expanding the polymeric material may be given to the film.
As described above, in the present invention, the plate can be used repeatedly; hence, use of conventional disposable heat-sensitive stencil sheets are not necessary. Thus, all the devices necessary for handling stencil sheets can be eliminated from conventionally used rotary stencil printing machines by applying the present plate to a printing drum of a rotary stencil printing machine with a proper master making function.
In accordance with still another aspect of the present invention, there is provided a stencil printing apparatus comprising an ink-permeable cylindrical printing drum which is rotary driven around its central axis and has the stencil printing plate according to the present invention on an outer circumferential surface thereof, a master making means which provides said film with a stimulus selected from heat and light so that said apertures are selectively expanded in accordance with a desired image, a squeegee means disposed to inscribe an inner circumferential surface of said printing drum such that an image forming material supplied to an inside of said printing drum is squeezed outwardly of said printing drum, and a pressing means which applies pressure to at least one of said printing drum and a printing sheet to bring them in close contact with each other while said printing sheet is being moved in synchronism with rotation of said printing drum, so that the image forming material is transferred to the printing sheet from the inside of the printing drum through the expanded apertures of the plate. To further facilitate regeneration of the plate, the stencil printing apparatus may further comprise a means for providing the plate with a stimulus which expands the polymeric material of the plate so that the expanded apertures of the plate are narrowed.